Magnetic tape having characterized magnetic layer

ABSTRACT

Provided is a magnetic tape in which an Ra measured regarding a surface of a magnetic layer is equal to or smaller than 1.8 nm, Int(110)/Int(114) of a hexagonal ferrite crystal structure obtained by an XRD analysis of the magnetic layer by using an In-Plane method is 0.5 to 4.0, a vertical squareness ratio of the magnetic tape is 0.65 to 1.00, full widths at half maximum of spacing distribution measured by optical interferometry regarding the surface of the back coating layer before and after performing a vacuum heating with respect to the magnetic tape are greater than 0 nm and equal to or smaller than 10.0 nm, and a difference between the spacings measured by optical interferometry regarding the surface of the back coating layer before and after performing the vacuum heating is greater than 0 nm and equal to or smaller than 8.0 nm.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. 119 to Japanese PatentApplication No. 2017-140024 filed on Jul. 19, 2017. The aboveapplication is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a magnetic tape.

2. Description of the Related Art

Magnetic recording media are divided into tape-shaped magnetic recordingmedia and disk-shaped magnetic recording media, and tape-shaped magneticrecording media, that is, magnetic tapes are mainly used for storagesuch as data back-up.

As the magnetic tapes, JP1989-60819A (JP-H01-60819A) discloses amagnetic tape including a back coating layer (described as a “backlayer” in JP1989-60819A (JP-H01-60819A)) on a surface side of anon-magnetic support opposite to a surface side provided with a magneticlayer.

SUMMARY OF THE INVENTION

In addition, in recent years, it is necessary that surface smoothness ofa magnetic layer is increased in a magnetic tape. This is because anincrease in surface smoothness of a magnetic layer causes improvement ofelectromagnetic conversion characteristics.

However, the inventors have made studies regarding a magnetic tapeincluding a back coating layer and found that, particularly, in amagnetic tape in which surface smoothness of a magnetic layer isincreased so that a center line average surface roughness Ra measuredregarding a surface of the magnetic layer is equal to or smaller than1.8 nm, a phenomenon in which an edge part of the magnetic tape isdamaged (hereinafter, referred to as “edge damage”) significantlyoccurs, after causing the magnetic tape to run in a drive. In regards tothis point, more specifically, the recording of information on themagnetic tape and/or reproducing the recorded information is performedby setting a magnetic tape cartridge in a drive, causing the magnetictape to run in the drive, and causing the magnetic head mounted on thedrive to come into contact with the surface of the magnetic layer forsliding. Since the magnetic tape is accommodated in the magnetic tapecartridge in a state of being wound around the reel, sending of themagnetic tape from the reel and winding thereof are performed during therunning of the magnetic tape in the drive. In a case where disorderedwinding occurs at the time of this winding, an edge of the magnetic tapehits against a flange or the like of a reel and the edge damage mayoccur. This edge damage may cause an increase in the number of errors atthe time of recording and/or a deterioration of miming stability.Accordingly, it is necessary that the disordered winding is prevented toreduce the edge damage.

Therefore, an aspect of the invention provides for a magnetic tape inwhich a center line average surface roughness Ra measured regarding asurface of the magnetic layer is equal to or smaller than 1.8 nm andoccurrence of edge damage is prevented.

According to one aspect of the invention, there is provided a magnetictape comprising: a non-magnetic support; a magnetic layer includingferromagnetic powder, non-magnetic powder, and a binding agent on onesurface side of the non-magnetic support; and a back coating layerincluding non-magnetic powder and a binding agent on the other surfaceside of the non-magnetic support, in which the ferromagnetic powder isferromagnetic hexagonal ferrite powder, a center line average surfaceroughness Ra measured regarding a surface of the magnetic layer(hereinafter, also referred to as a “magnetic layer surface roughnessRa”) is equal to or smaller than 1.8 nm, an intensity ratio(Int(110)/Int(114); hereinafter, also referred to as “X-ray diffraction(XRD) intensity ratio) of a peak intensity Int(110) of a diffractionpeak of a (110) plane with respect to a peak intensity Int(114) of adiffraction peak of a (114) plane of a hexagonal ferrite crystalstructure obtained by an X-ray diffraction analysis of the magneticlayer by using an In-Plane method is 0.5 to 4.0, a vertical squarenessratio of the magnetic tape is 0.65 to 1.00, the back coating layerincludes fatty acid ester, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe back coating layer before performing a vacuum heating with respectto the magnetic tape is greater than 0 nm and equal to or smaller than10.0 nm, a full width at half maximum of spacing distribution measuredby optical interferometry regarding the surface of the back coatinglayer after performing the vacuum heating with respect to the magnetictape is greater than 0 nm and equal to or smaller than 10.0 nm, and adifference (S_(after)−S_(before)) between a spacing S_(after) measuredby optical interferometry regarding the surface of the back coatinglayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the back coating layer before performing thevacuum heating with respect to the magnetic tape is greater than 0 nmand equal to or smaller than 8.0 nm.

In one aspect, the center line average surface roughness Ra measuredregarding the surface of the magnetic layer may be 1.2 nm to 1.8 nm.

In one aspect, the vertical squareness ratio of the magnetic tape may be0.65 to 0.90.

In one aspect, the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the backcoating layer before performing the vacuum heating with respect to themagnetic tape may be greater than 0 nm and equal to or smaller than 8.5nm.

In one aspect, the full width at half maximum of spacing distributionmeasured by optical interferometry regarding the surface of the backcoating layer after performing the vacuum heating with respect to themagnetic tape may be greater than 0 nm and equal to or smaller than 8.5nm.

In one aspect, the difference (S_(after)−S_(before)) between the spacingS_(after) measured by optical interferometry regarding the surface ofthe back coating layer after performing the vacuum heating with respectto the magnetic tape and the spacing S_(before) measured by opticalinterferometry regarding the surface of the back coating layer beforeperforming the vacuum heating with respect to the magnetic tape may begreater than 0 nm and equal to or smaller than 6.0 nm.

In one aspect, the non-magnetic powder included in the back coatinglayer may be one or more kinds of non-magnetic powder selected from thegroup consisting of inorganic powder and carbon black.

In one aspect, a content of the inorganic powder in the back coatinglayer may be greater than 50.0 parts by mass and equal to or smallerthan 100.0 parts by mass with respect to 100.0 parts by mass of a totalamount of the non-magnetic powder included in the back coating layer.

In one aspect, the magnetic tape may further comprise a non-magneticlayer including non-magnetic powder and a binding agent between thenon-magnetic support and the magnetic layer.

According to one aspect of the invention, it is possible to provide amagnetic tape which has high surface smoothness of a magnetic layer andin which occurrence of edge damage is prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram of a vibration impartingdevice used in examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the invention relates to a magnetic tape including: anon-magnetic support; a magnetic layer including ferromagnetic powder,non-magnetic powder, and a binding agent on one surface side of thenon-magnetic support; and a back coating layer including non-magneticpowder and a binding agent on the other surface side of the non-magneticsupport, in which the ferromagnetic powder is ferromagnetic hexagonalferrite powder, a center line average surface roughness Ra measuredregarding a surface of the magnetic layer is equal to or smaller than1.8 nm, an intensity ratio (Int(110)/Int(114)) of a peak intensityInt(110) of a diffraction peak of a (110) plane with respect to a peakintensity Int(114) of a diffraction peak of a (114) plane of a hexagonalferrite crystal structure obtained by an X-ray diffraction analysis ofthe magnetic layer by using an In-Plane method is 0.5 to 4.0, a verticalsquareness ratio of the magnetic tape is 0.65 to 1.00, the back coatinglayer includes fatty acid ester, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe back coating layer before performing a vacuum heating with respectto the magnetic tape is greater than 0 nm and equal to or smaller than10.0 nm, a full width at half maximum of spacing distribution measuredby optical interferometry regarding the surface of the back coatinglayer after performing the vacuum heating with respect to the magnetictape is greater than 0 nm and equal to or smaller than 10.0 nm, and adifference (S_(after)−S_(before)) between a spacing S_(after) measuredby optical interferometry regarding the surface of the back coatinglayer after performing the vacuum heating with respect to the magnetictape and a spacing S_(before) measured by optical interferometryregarding the surface of the back coating layer before performing thevacuum heating with respect to the magnetic tape is greater than 0 nmand equal to or smaller than 8.0 nm.

Hereinafter, the magnetic tape will be described more specifically. Thefollowing description includes a surmise of the inventors. The inventionis not limited to such a surmise. In addition, hereinafter, exemplarydescription may be made with reference to the drawings. However, theinvention is not limited to the exemplified aspects.

In the magnetic tape, even in a case where the magnetic layer surfaceroughness Ra is equal to or smaller than 1.8 nm, occurrence of edgedamage can be prevented. In regards to this point, the inventors haveconsidered as follows.

The inventors have considered that a reason for which the edge damagesignificantly occurs in a magnetic tape having the magnetic layersurface roughness Ra equal to or smaller than 1.8 nm, is because anunstable contact state between the surface of the magnetic layer and thesurface of the back coating layer, in a case of the winding, due to anincrease in surface smoothness of the magnetic layer. With respect tothis, the inventors have considered that, in the magnetic tape, the XRDintensity ratio, the vertical squareness ratio, and various valuesmeasured regarding the surface of the back coating layer set to be inthe respective ranges described above contribute to an increase instability of the contact state between the surface of the magnetic layerand the surfaces of the back coating layer, thereby preventingoccurrence of the edge damage occurred due to the disordered winding.This point will be described later in detail.

In the invention and the specification, the “surface of the magneticlayer” of the magnetic tape is identical to the surface of the magnetictape on the magnetic layer side. The “surface of the back coating layer”is identical to the surface of the magnetic tape on the back coatinglayer side. In the invention and the specification, the “ferromagnetichexagonal ferrite powder” means an aggregate of a plurality offerromagnetic hexagonal ferrite particles. The ferromagnetic hexagonalferrite particles are ferromagnetic particles having a hexagonal ferritecrystal structure. Hereinafter, particles (ferromagnetic hexagonalferrite particles) configuring the ferromagnetic hexagonal ferritepowder are also referred to as simply “particles”. The “aggregate” notonly includes an aspect in which particles configuring the aggregate aredirectly in contact with each other, but also includes an aspect inwhich a binding agent, an additive, or the like is sandwiched betweenthe particles. The points described above are also applied to variouspowders such as non-magnetic powder of the invention and thespecification, in the same manner.

In the invention and the specification, the description regardingdirections and angles (for example, vertical, orthogonal, parallel, andthe like) includes a range of errors allowed in the technical field ofthe invention, unless otherwise noted. For example, the range of errorsmeans a range of less than ±10° from an exact angle, and is preferablywithin ±5° and more preferably within ±3° from an exact angle.

In addition, hereinafter, the full width at half maximum (FWHM) ofspacing distribution measured by optical interferometry regarding thesurface of the back coating layer before performing the vacuum heatingwith respect to the magnetic tape is also referred to as “FWHM_(before)of the back coating layer” or “FWHM_(before)”, and the full width athalf maximum of spacing distribution measured by optical interferometryregarding the surface of the back coating layer after performing thevacuum heating with respect to the magnetic tape is also referred to as“FWHM_(after) of the back coating layer” or “FWHM_(after)”. In addition,the difference between a spacing S_(after) measured by opticalinterferometry regarding the surface of the back coating layer afterperforming the vacuum heating with respect to the magnetic tape and aspacing S_(before) measured by optical interferometry regarding thesurface of the back coating layer before performing the vacuum heatingwith respect to the magnetic tape is also referred to as the “difference(S_(after)−S_(before)) of the back coating layer” or the “difference(S_(after)−S_(before))”.

Magnetic Layer Surface Roughness Ra

The magnetic layer surface roughness Ra measured regarding the surfaceof the magnetic layer of the magnetic tape (magnetic layer surfaceroughness Ra) is equal to or smaller than 1.8 nm. It is preferable thatthe magnetic layer surface roughness Ra is equal to or smaller than 1.8nm, from a viewpoint of improving electromagnetic conversioncharacteristics. However, as described above, the edge damagesignificantly occurs in the magnetic tape having increased surfacesmoothness of the magnetic layer so that the magnetic layer surfaceroughness Ra becomes equal to or smaller than 1.8 nm. With respect tothis, in the magnetic tape, by setting the XRD intensity ratio, thevertical squareness ratio, the FWHM_(before) and the FWHM_(after)measured by optical interferometry regarding the surface of the backcoating layer, and the difference (S_(after)−S_(before)) to be in therespective ranges described above, occurrence of the edge damage can beprevented. From a viewpoint of further improving electromagneticconversion characteristics, low magnetic layer surface roughness Ra ispreferable. From this viewpoint, the magnetic layer surface roughness Racan be equal to or smaller than 1.7 nm or equal to or smaller than 1.6nm. In addition, the magnetic layer surface roughness Ra can be, forexample, equal to or greater than 1.2 nm or equal to or greater than 1.3nm. However, low magnetic layer surface roughness Ra is preferable, froma viewpoint of improving electromagnetic conversion characteristics, andthus, the magnetic layer surface roughness Ra may be lower than thevalue exemplified above.

The center line average surface roughness Ra measured regarding thesurface of the magnetic layer of the magnetic tape in the invention andthe specification is a value measured with an atomic force microscope(AFM) in a region having an area of 40 μm×40 μm of the surface of themagnetic layer. As an example of the measurement conditions, thefollowing measurement conditions can be used. The magnetic layer surfaceroughness Ra shown in examples which will be described later is a valueobtained by the measurement under the following measurement conditions.

The measurement is performed regarding the region of 40 μm×40 μm of thearea of the surface of the magnetic layer of the magnetic tape with anAFM (Nanoscope 4 manufactured by Veeco Instruments, Inc.) in a tappingmode. RTESP-300 manufactured by BRUKER is used as a probe, a scan speed(probe movement speed) is set as 40 μm/sec, and a resolution is set as512 pixel×512 pixel.

The magnetic layer surface roughness Ra can be controlled by awell-known method. For example, the magnetic layer surface roughness Racan be changed in accordance with the size of various powders includedin the magnetic layer (for example, ferromagnetic hexagonal ferritepowder, non-magnetic powder, and the like) or manufacturing conditionsof the magnetic tape. Thus, by adjusting these, it is possible to obtainthe magnetic tape having the magnetic layer surface roughness Ra equalto or smaller than 1.8 nm.

XRD Intensity Ratio and Vertical Squareness Ratio

Next, the XRD intensity ratio and the vertical squareness ratio will bedescribed.

The magnetic tape of the magnetic tape device includes ferromagnetichexagonal ferrite powder and non-magnetic powder in the magnetic layer.The non-magnetic powder in the magnetic layer can preferably function asan abrasive or a projection formation agent, as will be described laterin detail. However, it is thought that, in a case where the particles ofnon-magnetic powder (non-magnetic particles) present in the surface ofthe magnetic layer and/or the vicinity of the surface of the magneticlayer do not suitably sink into the magnetic layer with a force receivedfrom the magnetic head, at the time of the sliding of the surface of themagnetic layer and the magnetic head, chipping of the magnetic head(head chipping) may occur due to the contact with the particles of thenon-magnetic powder. On the other hand, it is thought that, in a casewhere the particles of the non-magnetic powder excessively sink into themagnetic layer, at the time of the sliding of the surface of themagnetic layer and the magnetic head, the area of the contact betweenthe surface of the magnetic layer and the magnetic head (real contact)increases, a force applied to the surface of the magnetic layer from themagnetic head at the time of the sliding becomes strong, and the surfaceof the magnetic layer is damaged, thereby causing the chipping of thesurface of the magnetic layer.

The inventors have surmised that scraps generated due to the headchipping and scraps generated due to the chipping of the surface of themagnetic layer described above are interposed between the surface of themagnetic layer and the surface of the back coating layer, therebydecreasing stability of a contact state between the surface of themagnetic layer and the surface of the back coating layer at the time ofwinding.

In regards to this point, the inventors have surmised that, particleswhich supports the particles of the non-magnetic powder put into themagnetic layer and affects a degree of the sinking (hereinafter, alsoreferred to as “former particles”) and particles which are considerednot to affect or slightly affects the sinking (hereinafter, alsoreferred to as “latter particles”) are included in the particlesconfiguring the ferromagnetic hexagonal ferrite powder included in themagnetic layer. It is considered that the latter particles are, forexample, fine particles generated due to partial chipping of particlesdue to a dispersion process performed at the time of preparing amagnetic layer forming composition.

The inventors have thought that, in the particles configuring theferromagnetic hexagonal ferrite powder (ferromagnetic hexagonal ferriteparticles) included in the magnetic layer, the former particles areparticles causing the diffraction peak in the X-ray diffraction analysisusing the In-Plane method, and since the latter particles are fine, thelatter particles do not or hardly affect the diffraction peak.Accordingly, it is surmised that it is possible to control a presencestate of the ferromagnetic hexagonal ferrite particles which supportsthe particles of the non-magnetic powder put into the magnetic layer andaffects a degree of the sinking, in the magnetic layer, based on theintensity of the diffraction peak caused by the X-ray diffractionanalysis of the magnetic layer using the In-Plane method, and as aresult, it is possible to control a degree of the sinking of theparticles of the non-magnetic powder. Specifically, the inventors havesurmised that, as the value of the XRD intensity ratio is small, theparticles of the non-magnetic powder easily sink, and as the valuethereof is great, the particles thereof hardly sink. The inventors havethought that, the sinking of the particles of the non-magnetic powdercan be suitably controlled to a degree that, the head chipping and thechipping of the surface of the magnetic layer can be prevented, bysetting the XRD intensity ratio to be 0.5 to 4.0. The inventors havesurmised that, this causes preventing a decrease in stability of thecontact state between the surface of the magnetic layer and the surfaceof the back coating layer at the time of the winding, due to the scrapsgenerated due to the head chipping and the scraps generated due to thesurface of the magnetic layer which are interposed between the surfaceof the magnetic layer and the surface of the back coating layer.

Meanwhile, the vertical squareness ratio is a ratio of residualmagnetization with respect to saturation magnetization measured in adirection vertical to the surface of the magnetic layer and this valuedecreases, as a value of the residual magnetization decreases. It issurmised that, since the latter particles are fine and hardly holdmagnetization, as a large amount of the latter particles is included inthe magnetic layer, the vertical squareness ratio tends to decrease.Accordingly, the inventors have thought that the vertical squarenessratio may be an index for the amount of the latter particles (fineparticles) present in the magnetic layer. In addition, the inventorshave surmised that, as a large amount of the fine particles is includedin the magnetic layer, hardness of the magnetic layer is decreased, thechipping of the surface of the magnetic layer easily occurs due to thecontact with the magnetic head and the like, the scraps generated due tothe chipping are interposed between the surface of the magnetic layerand the surface of the back coating layer, and accordingly, stability ofthe contact state between the surface of the magnetic layer and thesurface of the back coating layer at the time of the winding decreases.With respect to this, the inventors have thought that, in the magneticlayer having the vertical squareness ratio of 0.65 to 1.00, the chippingof the surface of the magnetic layer which is hardly performed due tothe decreased presence amount of the latter particles (fine particles)contributes to an increase in stability of the contact state between thesurface of the magnetic layer and the surface of the back coating layerat the time of the winding.

As described above, the invention have surmised that the XRD intensityratio of 0.5 to 4.0 and the vertical squareness ratio of 0.65 to 1.00causes an increase in stability of the contact state between the surfaceof the magnetic layer and the surface of the back coating layer at thetime of the winding, thereby contributing to the prevention ofoccurrence of the edge damage.

However, this is merely a surmise and the invention is not limitedthereto.

XRD Intensity Ratio

The XRD intensity ratio is obtained by the X-ray diffraction analysis ofthe magnetic layer including the ferromagnetic hexagonal ferrite powderby using the In-Plane method. Hereinafter, the X-ray diffractionanalysis performed by using the In-Plane method is also referred to as“In-Plane XRD”. The In-Plane XRD is performed by irradiating the surfaceof the magnetic layer with the X-ray by using a thin film X-raydiffraction device under the following conditions. A measurementdirection is a longitudinal direction of the magnetic tape.

Cu ray source used (output of 45 kV, 200 mA)

Scan conditions: 0.05 degree/step, 0.1 degree/min in a range of 20 to 40degrees

Optical system used: parallel optical system

Measurement method: 2θ_(χ) scan (X-ray incidence angle of 0.25°)

The values of the conditions are set values of the thin film X-raydiffraction device. As the thin film X-ray diffraction device, awell-known device can be used. As an example of the thin film X-raydiffraction device, Smart Lab manufactured by Rigaku Corporation. Asample to be subjected to the In-Plane XRD analysis is a tape sample cutout from the magnetic tape which is a measurement target, and the sizeand the shape thereof are not limited, as long as the diffraction peakwhich will be described later can be confirmed.

As a method of the X-ray diffraction analysis, thin film X-raydiffraction and powder X-ray diffraction are used. In the powder X-raydiffraction, the X-ray diffraction of the powder sample is measured,whereas, according to the thin film X-ray diffraction, the X-raydiffraction of a layer or the like formed on a substrate can bemeasured. The thin film X-ray diffraction is classified into theIn-Plane method and an Out-Of-Plane method. The X-ray incidence angle atthe time of the measurement is 5.00° to 90.00° in a case of theOut-Of-Plane method, and is generally 0.20° to 0.50°, in a case of theIn-Plane method. In the In-Plane XRD of the invention and thespecification, the X-ray incidence angle is 0.25° as described above. Inthe In-Plane method, the X-ray incidence angle is smaller than that inthe Out-Of-Plane method, and thus, a depth of penetration of the X-rayis shallow. Accordingly, according to the X-ray diffraction analysis byusing the In-Plane method (In-Plane XRD), it is possible to perform theX-ray diffraction analysis of a surface portion of a measurement targetsample. Regarding the tape sample, according to the In-Plane XRD, it ispossible to perform the X-ray diffraction analysis of the magneticlayer. The XRD intensity ratio is an intensity ratio (Int(110)/Int(114))of a peak intensity Int(110) of a diffraction peak of a (110) plane withrespect to a peak intensity Int(114) of a diffraction peak of a (114)plane of a hexagonal ferrite crystal structure, in X-ray diffractionspectra obtained by the In-Plane XRD. The term Int is used asabbreviation of intensity. In the X-ray diffraction spectra obtained byIn-Plane XRD (vertical axis: intensity, horizontal axis: diffractionangle 2θ_(χ) (degree)), the diffraction peak of the (114) plane is apeak at which the 2θ_(χ) is detected at 33 to 36 degrees, and thediffraction peak of the (110) plane is a peak at which the 2θ_(χ) isdetected at 29 to 32 degrees.

Among the diffraction plane, the (114) plane having a hexagonal ferritecrystal structure is positioned close to particles of the ferromagnetichexagonal ferrite powder (ferromagnetic hexagonal ferrite particles) inan easy-magnetization axial direction (c axis direction). In additionthe (110) plane having a hexagonal ferrite crystal structure ispositioned in a direction orthogonal to the easy-magnetization axialdirection.

The inventors have surmised that, in the X-ray diffraction spectraobtained by the In-Plane XRD, as the intensity ratio (Int(110)/Int(114);XRD intensity ratio) of the peak intensity Int(110) of the diffractionpeak of a (110) plane with respect to the peak intensity Int(114) of thediffraction peak of the (114) plane of a hexagonal ferrite crystalstructure increases, a large number of the former particles present in astate where a direction orthogonal to the easy-magnetization axialdirection is closer to a parallel state with respect to the surface ofthe magnetic layer is present in the magnetic layer, and as the XRDintensity ratio decreases, a small amount of the former particlespresent in such a state is present in the magnetic layer. It is thoughtthat a state where the XRD intensity ratio is 0.5 to 4.0 means a statewhere the former particles are suitably aligned in the magnetic layer.It is surmised that this causes an increase in stability of the contactstate between the surface of the magnetic layer and the surface of theback coating layer at the time of the winding, thereby contributing tothe prevention of occurrence of the edge damage. Details of the surmiseare as described above.

The XRD intensity ratio is preferably equal to or smaller than 3.5 andmore preferably equal to or smaller than 3.0, from a viewpoint offurther preventing occurrence of the edge damage. From the sameviewpoint, the XRD intensity ratio is preferably equal to or greaterthan 0.7 and more preferably equal to or greater than 1.0. The XRDintensity ratio can be, for example, controlled in accordance withprocess conditions of an alignment process performed in a manufacturingstep of the magnetic tape. As the alignment process, the homeotropicalignment process is preferably performed. The homeotropic alignmentprocess can be preferably performed by applying a magnetic fieldvertically to the surface of a coating layer of a magnetic layer formingcomposition in a wet state (undried state). As the alignment conditionsare reinforced, the value of the XRD intensity ratio tends to increase.As the process conditions of the alignment process, magnetic fieldstrength of the alignment process is used. The process conditions of thealignment process are not particularly limited. The process conditionsof the alignment process may be set so as that the XRD intensity ratioof 0.5 to 4.0 can be realized. As an example, the magnetic fieldstrength of the homeotropic alignment process can be 0.10 to 0.80 T or0.10 to 0.60 T. As dispersibility of the ferromagnetic hexagonal ferritepowder in the magnetic layer forming composition increases, the value ofthe XRD intensity ratio tends to increase by the homeotropic alignmentprocess.

Vertical Squareness Ratio

The vertical squareness ratio is a squareness ratio measured regarding amagnetic tape in a vertical direction. The “vertical direction”described regarding the squareness ratio is a direction orthogonal tothe surface of the magnetic layer. That is, regarding the magnetic tape,the vertical direction is a direction orthogonal to a longitudinaldirection of the magnetic tape. The vertical squareness ratio ismeasured by using an oscillation sample type magnetic-flux meter.Specifically, the vertical squareness ratio of the invention and thespecification is a value obtained by sweeping an external magnetic fieldin the magnetic tape at a measurement temperature of 23° C.±1° C. in theoscillation sample type magnetic-flux meter, under conditions of amaximum external magnetic field of 1194 kA/m (15 kOe) and a scan speedof 4.8 kA/m/sec (60 Oe/sec), and is a value after diamagnetic fieldcorrection. The measurement value is obtained as a value obtained bysubtracting magnetization of a sample probe of the oscillation sampletype magnetic-flux meter as background noise.

The vertical squareness ratio of the magnetic tape is equal to orgreater than 0.65. The inventors have surmised that the verticalsquareness ratio of the magnetic tape is an index for the presenceamount of the latter particles (fine particles) described above. It isthought that, in the magnetic layer in which the vertical squarenessratio of the magnetic tape is equal to or greater than 0.65, thepresence amount of such fine particles is small. As described above indetail, the inventors have surmised that this also contributes toprevention of the occurrence of the edge damage.

From a viewpoint of further preventing the occurrence of the edgedamage, the vertical squareness ratio is preferably equal to or greaterthan 0.68, more preferably equal to or greater than 0.70, even morepreferably equal to or greater than 0.73, and still more preferablyequal to or greater than 0.75. In addition, in principle, a maximumvalue of the squareness ratio is 1.00. Accordingly, the verticalsquareness ratio of the magnetic tape is equal to or smaller than 1.00.The vertical squareness ratio may be, for example, equal to or smallerthan 0.95, equal to or smaller than 0.90, equal to or smaller than 0.87,or equal to or smaller than 0.85. It is thought that, a great value ofthe vertical squareness ratio is preferable, from a viewpoint ofdecreasing the amount of the fine latter particles in the magnetic layerand further preventing the occurrence of the edge damage. Therefore, thevertical squareness ratio may be greater than the value exemplifiedabove.

The inventors have considered that, in order to set the verticalsquareness ratio to be equal to or greater than 0.65, it is preferableto prevent occurrence of fine particles due to partial chipping of theparticles in a preparation step of the magnetic layer formingcomposition. A specific method for preventing the occurrence of chippingwill be described later.

FWHM_(before) and FWHM_(after) of the back coating layer and difference(S_(after)−S_(before))

The FWHM_(after) and the spacing S_(after) for obtaining the difference(S_(after)−S_(before)) are values obtained after performing vacuumheating with respect to the magnetic tape. In the invention and thespecification, the “vacuum heating” of the magnetic tape is performed byholding the magnetic tape in an environment of a pressure of 200 Pa to0.01 MPa and at an atmosphere temperature of 70° C. to 90° C. for 24hours.

In the invention and the specification, the spacing measured by opticalinterferometry regarding the surface of the back coating layer of themagnetic tape is a value measured by the following method.

In a state where the magnetic tape and a transparent plate-shaped member(for example, glass plate or the like) are overlapped onto each other sothat the surface of the back coating layer of the magnetic tape facesthe transparent plate-shaped member, a pressing member is pressedagainst the side of the magnetic tape opposite to the back coating layerside at pressure of 5.05×10⁴ N/m (0.5 atm). In this state, the surfaceof the back coating layer of the magnetic tape is irradiated with lightthrough the transparent plate-shaped member (irradiation region: 150,000to 200,000 μm²), and a spacing (distance) between the surface of theback coating layer of the magnetic tape and the surface of thetransparent plate-shaped member is acquired based on intensity (forexample, contrast of interference fringe image) of interference lightgenerated due to a difference in a light path between reflected lightfrom the surface of the back coating layer of the magnetic tape andreflected light from the surface of the transparent plate-shaped memberon the magnetic tape side. The light emitted here is not particularlylimited. In a case where the emitted light is light having an emissionwavelength over a comparatively wide wavelength range as white lightincluding light having a plurality of wavelengths, a member having afunction of selectively cutting light having a specific wavelength or awavelength other than wavelengths in a specific wavelength range, suchas an interference filter, is disposed between the transparentplate-shaped member and a light receiving section which receivesreflected light, and light at some wavelengths or in some wavelengthranges of the reflected light is selectively incident to the lightreceiving section. In a case where the light emitted is light (so-calledmonochromatic light) having a single luminescence peak, the memberdescribed above may not be used. The wavelength of light incident to thelight receiving section can be set to be 500 to 700 nm, for example.However, the wavelength of light incident to the light receiving sectionis not limited to be in the range described above. In addition, thetransparent plate-shaped member may be a member having transparencythrough which emitted light passes, to the extent that the magnetic tapeis irradiated with light through this member and interference light isobtained.

The measurement described above can be performed by using a commerciallyavailable tape spacing analyzer (TSA) such as Tape Spacing Analyzermanufactured by Micro Physics, Inc., for example. The spacingmeasurement of the examples was performed by using Tape Spacing Analyzermanufactured by Micro Physics, Inc.

In addition, the full width at half maximum of spacing distribution ofthe invention and the specification is a full width at half maximum(FWHM), in a case where the interference fringe image obtained by themeasurement of the spacing described above is divided into 300,000points, a spacing of each point (distance between the surface of theback coating layer of the magnetic tape and the surface of thetransparent plate-shaped member on the magnetic tape side) is acquired,this spacing is shown with a histogram, and this histogram is fit withGaussian distribution.

Further, the difference (S_(after)−S_(before)) is a value obtained bysubtracting a mode before the vacuum heating from a mode after thevacuum heating of the 300,000 points.

The inventors have surmised as the following (1) and (2) for the variousvalues regarding the back coating layer.

(1) The inventors have thought that the value of the difference(S_(after)−S_(before)) can be an index for a thickness of a liquid filmformed of fatty acid ester included in the back coating layer, on thesurface of the back coating layer. Details thereof are as describedbelow.

A lubricant is generally divided broadly into a fluid lubricant and aboundary lubricant and fatty acid ester is known as a component whichcan function as a fluid lubricant. It is considered that fatty acidester can protect the back coating layer by forming a liquid film on thesurface of the back coating layer. In addition, it is thought that, in acase where the magnetic tape is wound around a reel and the surface ofthe back coating layer is in contact with the surface of the magneticlayer, the liquid film of fatty acid ester can cause a force (meniscusforce) of pulling both surfaces between both surfaces due to a meniscus(liquid crosslinking). It is surmised that this contributes to anincrease in stability of the contact state between the surface of theback coating layer and the surface of the magnetic layer at the time ofthe winding. However, it is thought that, in a case where an excessiveamount of fatty acid ester is present on the surface of the back coatinglayer, the meniscus force is strongly applied, and thereby causing thesticking causing a decrease in stability of the contact state.

In regards to this point, it is thought that the difference(S_(after)−S_(before)) of a spacing between a state after the vacuumheating (state in which a liquid film of fatty acid ester is volatilizedand removed) and a state before the vacuum heating (state in which theliquid film of fatty acid ester is present) can be an index of thethickness of the liquid film formed of fatty acid ester on the surfaceof the back coating layer, because the fatty acid ester is a componenthaving properties of volatilizing by vacuum heating. The inventors havesurmised that the presence of the liquid film of fatty acid ester on thesurface of the back coating layer so that the difference(S_(after)−S_(before)) is greater than 0 nm and equal to or smaller than8.0 nm, brings the surface of the back coating layer into contact withthe surface of the magnetic layer at the time of the winding in a stablecontact state, while preventing sticking.

(2) In addition, the invention have thought that the FWHM_(before) andFWHM_(after) which are further set in the ranges in the surface of theback coating layer having the difference (S_(after)−S_(before)) in therange described above, contributes to applying of the meniscus forcepromoting the prevention of disordered winding between the surface ofthe back coating layer and the surface of the magnetic layer. In regardsto this point, a smaller value of the full width at half maximum ofspacing distribution measured by optical interferometry means that avariation in the values of the spacing measured on each part of thesurface of the measurement target is small. It is thought that a reasonfor the variation in the values of the spacing on the surface of theback coating layer of the magnetic tape is a variation in surface shapeof the back coating layer (for example, a variation due to a dispersionstate of the non-magnetic powder included in the back coating layer) anda variation in thickness of the liquid film formed of fatty acid ester.It is thought that the FWHM_(before) measured before the vacuum heating,that is, in a state where the liquid film of fatty acid ester is presenton the surface of the back coating layer becomes great, as the variationin the surface shape of the back coating layer and the variation in thethickness of the liquid film of fatty acid ester are great.Particularly, the FWHM_(before) is greatly affected by the variation inthe thickness of the liquid film of fatty acid ester. In contrast, theinventors have surmised that the FWHM_(after) measured after the vacuumheating, that is, in a state where the liquid film of fatty acid esteris removed from the surface of the back coating layer, becomes great, asthe variation in the surface shape of the back coating layer is great.That is, it is thought that small FWHM_(before) and FWHM_(after) mean asmall variation in the surface shape of the back coating layer and asmall variation in the thickness of the liquid film of fatty acid esteron the surface of the back coating layer. The inventors have surmisedthat an increase in uniformity of the surface shape of the back coatinglayer and uniformity in the thickness of the liquid film of fatty acidester so that the FWHM_(before) and FWHM_(after) are greater than 0 nmand equal to or smaller than 10.0 nm, contributes to applying of themeniscus force promoting prevention of the disordered winding betweenthe surface of the back coating layer and the surface of the magneticlayer having the difference (S_(after)−S_(before)) in the rangedescribed above.

However, the (1) and (2) are merely surmised and the invention is notlimited thereto.

FWHM_(before) and FWHM_(after)

Both of the FWHM_(before) measured before the vacuum heating and theFWHM_(after) measured after the vacuum heating in the surface of theback coating layer of the magnetic tape are greater than 0 nm and equalto or smaller than 10.0 nm. As described above, the inventors havesurmised that the FWHM_(before) and FWHM_(after) in the range describedabove contribute to an increase in stability of the contact statebetween the surface of the back coating layer and the surface of themagnetic layer at the time of the winding. From a viewpoint of furtherincreasing stability of the contact state, FWHM_(before) andFWHM_(after) preferably equal to or smaller than 9.0 nm, more preferablyequal to or smaller 8.5 nm, even more preferably equal to or smallerthan 8.0 nm, still preferably equal to or smaller than 7.0 nm, stillmore preferably equal to or smaller than 6.0 nm, and still even morepreferably equal to or smaller than 5.0 nm. The FWHM_(before) andFWHM_(after) can be, for example, equal to or greater than 1.0 nm orequal to or greater than 2.0 nm. From a viewpoint of preventing theoccurrence of the edge damage, small values of the FWHM_(before) andFWHM_(after) tend to be preferable. Accordingly, the FWHM_(before) andFWHM_(after) may be lower than the lower limit exemplified above.

The FWHM_(before) measured before the vacuum heating can be decreasedmainly by decreasing the variation in the thickness of the liquid filmof fatty acid ester. An example of a specific method will be describedlater. Meanwhile, the FWHM_(after) measured after the vacuum heating canbe decreased by decreasing the variation in the surface shape of theback coating layer. In order to realize the decrease described above, itis preferable that dispersibility of the non-magnetic powder in a backcoating layer forming composition is improved. The dispersibility canbe, for example, adjusted by the kind of the non-magnetic powder usedfor forming the back coating layer and by a mixing ratio or the like, ina case of including two or more kinds of the non-magnetic powders. Anexample of a specific method will be described later.

Difference (S_(after)−S_(before))

The difference (S_(after)−S_(before)) of the spacings before and afterthe vacuum heating measured regarding the surface of the back coatinglayer of the magnetic tape is greater than 0 nm and equal to or smallerthan 8.0 nm. From a viewpoint of further preventing the occurrence ofthe edge damage, the difference (S_(after)−S_(before)) is preferablyequal to or greater than 0.1 nm, more preferably equal to or greaterthan 1.0 nm, and even more preferably equal to or greater than 1.5 nm.In addition, from the same viewpoint, the difference(S_(after)−S_(before)) is preferably equal to or smaller than 7.0 nm,more preferably equal to or smaller than 6.0 nm, even more preferablyequal to or smaller than 5.0 nm, and still more preferably equal to orsmaller than 4.0 nm. The difference (S_(after)−S_(before)) can becontrolled by the amount of fatty acid ester added to a back coatinglayer forming composition. As the amount of fatty acid ester added to aback coating layer forming composition increases, the difference(S_(after)−S_(before)) tends to increase.

Hereinafter, the magnetic tape will be described more specifically.

Magnetic Layer

Ferromagnetic Powder

The magnetic layer of the magnetic tape includes ferromagnetic hexagonalferrite powder as ferromagnetic powder. Regarding the ferromagnetichexagonal ferrite powder, a magnetoplumbite type (also referred to as an“M type”), a W type, a Y type, and a Z type are known as the crystalstructure of the hexagonal ferrite. The ferromagnetic hexagonal ferritepowder included in the magnetic layer may have any crystal structure. Inaddition, an iron atom and a divalent metal atom are included in thecrystal structure of the hexagonal ferrite, as constituent atoms. Thedivalent metal atom is a metal atom which may become divalent cations asions, and examples thereof include a barium atom, a strontium atom, analkali earth metal atom such as calcium atom, and a lead atom. Forexample, the hexagonal ferrite including a barium atom as the divalentmetal atom is a barium ferrite, and the hexagonal ferrite including astrontium atom is a strontium ferrite. In addition, the hexagonalferrite may be a mixed crystal of two or more hexagonal ferrites. As anexample of the mixed crystal, a mixed crystal of the barium ferrite andthe strontium ferrite can be used.

As an index for a particle size of the ferromagnetic hexagonal ferritepowder, an activation volume can be used. The “activation volume” is aunit of magnetization reversal. Regarding the activation volumedescribed in the invention and the specification, magnetic field sweeprates of a coercivity Hc measurement part at time points of 3 minutesand 30 minutes are measured by using an oscillation sample typemagnetic-flux meter in an environment of an atmosphere temperature 23°C.±1° C., and the activation volume is a value acquired from thefollowing relational expression of He and an activation volume V.Hc=2 Ku/Ms {1−[(kT/KuV)ln(At/0.693)]^(1/2)}

[In the expression, Ku: anisotropy constant, Ms: saturationmagnetization, k: Boltzmann's constant, T: absolute temperature, V:activation volume, A: spin precession frequency, and t: magnetic fieldreversal time]

As a method for achieving high-density recording, a method of decreasinga particle size of ferromagnetic powder included in a magnetic layer andincreasing a filling percentage of the ferromagnetic powder of themagnetic layer is used. From this viewpoint, the activation volume ofthe ferromagnetic hexagonal ferrite powder is preferably equal to orsmaller than 2,500 nm³, more preferably equal to or smaller than 2,300nm³, and even more preferably equal to or smaller than 2,000 nm³.Meanwhile, from a viewpoint of stability of magnetization, theactivation volume is, for example, preferably equal to or greater than800 nm³, more preferably equal to or greater than 1,000 nm³, and evenmore preferably equal to or greater than 1,200 nm³.

The shape of the particle configuring the ferromagnetic hexagonalferrite powder is specified by imaging the ferromagnetic hexagonalferrite powder at a magnification ratio of 100,000 with a transmissionelectron microscope, and tracing an outline of a particle (primaryparticle) with a digitizer on a particle image obtained by printing theimage on printing paper so that the total magnification of 500,000. Theprimary particle is an independent particle which is not aggregated. Theimaging with a transmission electron microscope is performed by a directmethod with a transmission electron microscope at an accelerationvoltage of 300 kV. The transmission electron microscope observation andmeasurement can be, for example, performed with a transmission electronmicroscope H-9000 manufactured by Hitachi, Ltd. and image analysissoftware KS-400 manufactured by Carl Zeiss. Regarding the shape of theparticle configuring the ferromagnetic hexagonal ferrite powder, a“planar shape” is a shape having two plate surfaces facing each other.Meanwhile, among the shapes of the particles not having such a platesurface, a shape having distinguished long axis and short axis is an“elliptical shape”. The long axis is determined as an axis (linear line)having the longest length of the particle. In contrast, the short axisis determined as an axis having the longest length of the particle in alinear line orthogonal to the long axis. A shape not havingdistinguished long axis and short axis, that is, a shape in which thelength of the long axis is the same as the length of the short axis is a“sphere shape”. From the shapes, a shape in which the long axis and theshort axis are hardly specified, is called an undefined shape. Theimaging with a transmission electron microscope for specifying theshapes of the particles is performed without performing the alignmentprocess with respect to the imaging target powder. The shape of theferromagnetic hexagonal ferrite powder used for the preparation of themagnetic layer forming composition and the ferromagnetic hexagonalferrite powder included in the magnetic layer may be any one of theplanar shape, the elliptical shape, the sphere shape, and the undefinedshape.

An average particle size of various powders disclosed in the inventionand the specification is an arithmetical mean of the values obtainedregarding randomly extracted 500 particles by using the particle imagewhich is captured as described above. The average particle size shown inthe examples which will be described later is a value obtained by usingtransmission electron microscope H-9000 manufactured by Hitachi, Ltd. asthe transmission electron microscope and image analysis software KS-400manufactured by Carl Zeiss as the image analysis software.

For details of the ferromagnetic hexagonal ferrite powder, descriptionsdisclosed in paragraphs 0134 to 0136 of JP2011-216149A can be referredto, for example.

The content (filling percentage) of the ferromagnetic hexagonal ferritepowder of the magnetic layer is preferably 50% to 90% by mass and morepreferably 60% to 90% by mass. The components other than theferromagnetic hexagonal ferrite powder of the magnetic layer are atleast a binding agent and non-magnetic powder, and one or more kinds ofadditives can be randomly included. A high filling percentage of theferromagnetic hexagonal ferrite powder of the magnetic layer ispreferable, from a viewpoint of improving recording density.

Binding Agent and Curing Agent

The magnetic tape is a coating type magnetic tape, and the magneticlayer includes a binding agent. The binding agent is one or more kindsof resin. As the binding agent, various resins normally used as abinding agent of the coating type magnetic recording medium can be used.For example, as the binding agent, a resin selected from a polyurethaneresin, a polyester resin, a polyamide resin, a vinyl chloride resin, anacrylic resin obtained by copolymerizing styrene, acrylonitrile, ormethyl methacrylate, a cellulose resin such as nitrocellulose, an epoxyresin, a phenoxy resin, and a polyvinylalkylal resin such as polyvinylacetal or polyvinyl butyral can be used alone or a plurality of resinscan be mixed with each other to be used. Among these, a polyurethaneresin, an acrylic resin, a cellulose resin, and a vinyl chloride resinare preferable. These resins may be a homopolymer or a copolymer. Theseresins can be used as the binding agent even in the back coating layerand/or the non-magnetic layer which will be described later. For thebinding agent described above, description disclosed in paragraphs 0028to 0031 of JP2010-24113A can be referred to. An average molecular weightof the resin used as the binding agent can be, for example, 10,000 to200,000 as a weight-average molecular weight. The weight-averagemolecular weight of the invention and the specification is a valueobtained by performing polystyrene conversion of a value measured by gelpermeation chromatography (GPC). As the measurement conditions, thefollowing conditions can be used. The weight-average molecular weightshown in examples which will be described later is a value obtained byperforming polystyrene conversion of a value measured under thefollowing measurement conditions.

GPC device: HLC-8120 (manufactured by Tosoh Corporation)

Column: TSK gel Multipore HXL-M (manufactured by Tosoh Corporation, 7.8mmID (inner diameter)×30.0 cm)

Eluent: Tetrahydrofuran (THF)

A curing agent can also be used together with a resin which can be usedas the binding agent. As the curing agent, in one aspect, athermosetting compound which is a compound in which a curing reaction(crosslinking reaction) proceeds due to heating can be used, and inanother aspect, a photocurable compound in which a curing reaction(crosslinking reaction) proceeds due to light irradiation can be used.At least a part of the curing agent is included in the magnetic layer ina state of being reacted (crosslinked) with other components such as thebinding agent, by proceeding the curing reaction in the magnetic layerforming step. In a case where a composition used for forming otherlayers such as the back coating layer forming composition includes acuring agent, the same applies to a layer formed by using thiscomposition. The preferred curing agent is a thermosetting compound,polyisocyanate is suitable. For details of the polyisocyanate,descriptions disclosed in paragraphs 0124 and 0125 of JP2011-216149A canbe referred to, for example. The amount of the curing agent can be, forexample, 0 to 80.0 parts by mass with respect to 100.0 parts by mass ofthe binding agent in the magnetic layer forming composition, and ispreferably 50.0 to 80.0 parts by mass, from a viewpoint of improvementof strength of the magnetic layer.

Non-Magnetic Powder

Examples of non-magnetic powder include in the magnetic layer includenon-magnetic powder which can function as a projection formation agentwhich forms projections suitably protruded from the surface of themagnetic layer (for example, referred to as a “projection formationagent”), and non-magnetic powder which can function as an abrasive (forexample, referred to as an “abrasive”). The inventors have surmisedthat, in the magnetic layer having the XRD intensity ratio of 0.5 to4.0, the sinking of the particles of the non-magnetic powder into themagnetic layer which can be suitably controlled, causes prevention ofthe occurrence of the edge damage. Details of such a surmise are asdescribed above.

As the projection formation agent which is one aspect of thenon-magnetic powder, various non-magnetic powders normally used as aprojection formation agent can be used. These may be inorganicsubstances or organic substances. In one aspect, from a viewpoint ofhomogenization of friction properties, particle size distribution of theprojection formation agent is not polydispersion having a plurality ofpeaks in the distribution and is preferably monodisperse showing asingle peak. From a viewpoint of availability of monodisperse particles,the projection formation agent is preferably powder of inorganicsubstances (inorganic powder). Examples of the inorganic powder includepowder of inorganic oxide such as metal oxide, metal carbonate, metalsulfate, metal nitride, metal carbide, and metal sulfide, and powder ofinorganic oxide is preferable. The projection formation agent is morepreferably colloid particles and even more preferably inorganic oxidecolloid particles. In addition, from a viewpoint of availability ofmonodisperse particles, the inorganic oxide configuring the inorganicoxide colloid particles are preferably silicon dioxide (silica). Theinorganic oxide colloid particles are more preferably colloidal silica(silica colloid particles). In the invention and the specification, the“colloid particles” are particles which are not precipitated anddispersed to generate a colloidal dispersion, in a case where 1 g of theparticles is added to 100 mL of at least one organic solvent of at leastmethyl ethyl ketone, cyclohexanone, toluene, or ethyl acetate, or amixed solvent including two or more kinds of the solvent described aboveat a random mixing ratio. In addition, in another aspect, the projectionformation agent is preferably carbon black.

An average particle size of the projection formation agent is, forexample, 30 to 300 nm and is preferably 40 to 200 nm.

The abrasive which is another aspect of the non-magnetic powder ispreferably non-magnetic powder having Mohs hardness exceeding 8 and morepreferably non-magnetic powder having Mohs hardness equal to or greaterthan 9. A maximum value of Mohs hardness is 10 of diamond. Specifically,powders of alumina (Al₂O₃), silicon carbide, boron carbide (B₄C), SiO₂,TiC, chromium oxide (Cr₂O₃), cerium oxide, zirconium oxide (ZrO₂), ironoxide, diamond, and the like can be used, and among these, aluminapowder such as α-alumina and silicon carbide powder are preferable. Inaddition, regarding the particle size of the abrasive, a specificsurface area which is an index for the particle size is, for example,equal to or greater than 14 m²/g, and is preferably 16 m²/g and morepreferably 18 m²/g. Further, the specific surface area of the abrasivecan be, for example, equal to or smaller than 40 m²/g. The specificsurface area is a value obtained by a nitrogen adsorption method (alsoreferred to as a Brunauer-Emmett-Teller (BET) 1 point method), and is avalue measured regarding primary particles. Hereinafter, the specificsurface area obtained by such a method is also referred to as a BETspecific surface area.

In addition, from a viewpoint that the projection formation agent andthe abrasive can exhibit the functions thereof in more excellent manner,the content of the projection formation agent in the magnetic layer ispreferably 1.0 to 4.0 parts by mass and more preferably 1.5 to 3.5 partsby mass with respect to 100.0 parts by mass of the ferromagnetichexagonal ferrite powder. Meanwhile, the content of the abrasive in themagnetic layer is preferably 1.0 to 20.0 parts by mass, more preferably3.0 to 15.0 parts by mass, and even more preferably 4.0 to 10.0 parts bymass with respect to 100.0 parts by mass of the ferromagnetic hexagonalferrite powder.

Other Components

The magnetic layer may include one or more kinds of additives, ifnecessary, together with the various components described above. As theadditives, a commercially available product can be suitably selected andused according to the desired properties. Alternatively, a compoundsynthesized by a well-known method can be used as the additives. As theadditives, the curing agent described above is used as an example. Inaddition, examples of the additive which can be included in the magneticlayer include a lubricant, a dispersing agent, a dispersing assistant,an antibacterial agent, an antistatic agent, and an antioxidant. Forexample, as the dispersing agent, a well-known dispersing agent such asa carboxy group-containing compound or a nitrogen-containing compoundcan be used. For example, the nitrogen-containing compound may be any ofa primary amine represented by NH₂R, a secondary amine represented byNHR₂, and a tertiary amine represented by NR₃. In the above description,R represents a random structure configuring the nitrogen-containingcompound, and a plurality of Rs may be the same as each other ordifferent from each other. The nitrogen-containing compound may be acompound (polymer) having a plurality of repeating structure in amolecule. It is thought that a nitrogen-containing part of thenitrogen-containing compound which functions as an adsorption part tothe surface of the particle of the ferromagnetic hexagonal ferritepowder is a reason why the nitrogen-containing compound can function asthe dispersing agent. As the carboxy group-containing compound, fattyacid such as oleic acid can be used, for example. It is thought that acarboxy group which functions as an adsorption part to the surface ofthe particle of the ferromagnetic hexagonal ferrite powder is a reasonwhy the carboxy group-containing compound can function as the dispersingagent. It is also preferable to use the carboxy group-containingcompound and the nitrogen-containing compound in combination.

As an example of the additive which can be used in the magnetic layerincluding the abrasive, a dispersing agent disclosed in paragraphs 0012to 0022 of JP2013-131285A can be used as a dispersing agent forimproving dispersibility of the abrasive of the magnetic layer formingcomposition. It is preferable to improve dispersibility of thenon-magnetic powder such as the abrasive in the magnetic layer formingcomposition, in order to decrease the magnetic layer surface roughnessRa.

Back Coating Layer

Fatty Acid Ester

The magnetic tape includes fatty acid ester in the back coating layer.The surmise of the inventors regarding the fatty acid ester, thedifference (S_(after)−S_(before)), the FWHM_(before), and theFWHM_(after) is as described above.

The fatty acid ester may be included in the back coating layer alone asone type or two or more types thereof may be included therein. Examplesof fatty acid ester include esters of lauric acid, myristic acid,palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid,behenic acid, erucic acid, and elaidic acid. Specific examples thereofinclude butyl myristate, butyl palmitate, butyl stearate (butylstearate), neopentyl glycol dioleate, sorbitan monostearate, sorbitandistearate, sorbitan tristearate, oleyl oleate, isocetyl stearate,isotridecyl stearate, octyl stearate, isooctyl stearate, amyl stearate,and butoxyethyl stearate.

The content of fatty acid ester in the back coating layer is, forexample, 0.1 to 10.0 parts by mass and is preferably 1.0 to 5.0 parts bymass with respect to 100.0 parts by mass of non-magnetic powder includedin the back coating layer. In a case of using two or more kinds ofdifferent fatty acid esters as the fatty acid ester, the content thereofis the total content thereof. In the invention and the specification, agiven component may be used alone or used in combination of two or morekinds thereof, unless otherwise noted. In a case of using two or morekinds of the given components, the content of this component is thetotal content of the two or more kinds thereof, unless otherwise noted.

Other Lubricants

The magnetic tape includes fatty acid ester which is one kind oflubricants in the back coating layer, and may or may not includelubricants other than fatty acid ester in the back coating layer. As thelubricant other than fatty acid ester, fatty acid or fatty acid amidecan be used. The fatty acid and fatty acid amide are generally known asa component which can function as a boundary lubricant.

Examples of fatty acid include lauric acid, myristic acid, palmiticacid, stearic acid, oleic acid, linoleic acid, linolenic acid, behenicacid, erucic acid, and elaidic acid, and stearic acid, myristic acid,and palmitic acid are preferable, and stearic acid is more preferable.Fatty acid may be included in the back coating layer in a state of saltsuch as metal salt.

As fatty acid amide, amide of various fatty acid described above isused, and examples thereof include lauric acid amide, myristic acidamide, palmitic acid amide, and stearic acid amide.

In a case of using fatty acid and a derivative of fatty acid (ester andamide) in combination, a part derived from fatty acid of the fatty acidderivative preferably has a structure which is the same as or similar tothat of fatty acid used in combination. As an example, in a case ofusing stearic acid as fatty acid, it is preferable to use stearic acidester and/or stearic acid amide.

The content of fatty acid in the back coating layer is, for example, 0to 10.0 parts by mass, preferably 0.1 to 10.0 parts by mass, and morepreferably 1.0 to 7.0 parts by mass, with respect to 100.0 parts by massof the non-magnetic powder included in the back coating layer. Thecontent of fatty acid amide in the back coating layer is, for example, 0to 3.0 parts by mass, preferably 0 to 2.0 parts by mass, and morepreferably 0 to 1.0 part by mass with respect to 100.0 parts by mass ofthe non-magnetic powder included in the back coating layer.

The various lubricants described above may be included in the magneticlayer and/or the non-magnetic layer which is randomly provided.Regarding the kind and/or the content of the lubricant in each layer, awell-known technology regarding the list of each layer can be used.

Non-Magnetic Powder

As non-magnetic powder including in the back coating layer, any one orboth of carbon black and non-magnetic powder other than the carbon blackcan be used. As the non-magnetic powder other than the carbon black,inorganic powder can be used. Examples of the inorganic powder includeinorganic powder of iron oxide such as α-iron oxide, titanium oxide suchas titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO₂,SiO₂, Cr₂O₃, α-alumina, β-alumina, γ-alumina, goethite, corundum,silicon nitride, titanium carbide, magnesium oxide, boron nitride,molybdenum disulfide, copper oxide, MgCO₃, CaCO₃, BaCO₃, SrCO₃, BaSO₄,and silicon carbide. The preferable inorganic powder is inorganic oxidepowder, more preferably α-iron oxide and titanium oxide, and even morepreferably α-iron oxide. For the non-magnetic powder included in theback coating layer, the description which will be described laterregarding the non-magnetic powder included in the non-magnetic layer canbe referred to.

Generally, the inorganic powder tends to have excellent dispersibilityin the back coating layer forming composition, compared to that ofcarbon black. An increase in dispersibility of the non-magnetic powderin the back coating layer forming composition can contribute to adecrease in variation of the surface shape of the back coating layer.Accordingly, as a method of adjusting the FWHM_(after) measured afterthe vacuum heating, which is considered to become a small value, as thevariation in the surface shape of the back coating layer decreases, amethod of adjusting the kind of the non-magnetic powder included in theback coating layer, and a mixing ratio, in a case of including two ormore kinds of the non-magnetic powders can be used. For example, as mainpowder of the non-magnetic powder of the back coating layer(non-magnetic powder, the largest amount of which is included based onmass, among the non-magnetic powder), the inorganic powder is preferablyused. In a case where the non-magnetic powder included in the backcoating layer is one or more kinds of the non-magnetic powder selectedfrom the group consisting of the inorganic powder and carbon black, thecontent of the inorganic powder with respect to 100.0 parts by mass of atotal amount of the non-magnetic powder is preferably greater than 50.0parts by mass and equal to or smaller than 100.0 parts by mass, morepreferably 60.0 parts by mass to 100.0 parts by mass, even morepreferably 70.0 parts by mass to 100.0 parts by mass, and still morepreferably 80.0 parts by mass to 100.0 parts by mass. In addition, forthe content (filling percentage) of the non-magnetic powder in the backcoating layer, the description which will be described later regardingthe non-magnetic powder of the non-magnetic layer can be referred to.

An average particle size of the non-magnetic powder can be, for example,10 to 200 nm. An average particle size of the inorganic powder ispreferably 50 to 200 nm and more preferably 80 to 150 nm. Meanwhile, anaverage particle size of the carbon black is preferably 10 to 50 nm andmore preferably 15 to 30 nm.

In addition, the dispersibility of the non-magnetic powder in the backcoating layer forming composition can be increased by using a well-knowndispersing agent, reinforcing dispersion conditions, and the like.

A preferable aspect of a method of adjusting FWHM_(before) measuredbefore the vacuum heating will be described later.

Other Components

The back coating layer further includes a binding agent and can randomlyinclude well-known additives. For other details of the binding agent andadditives of the back coating layer, a well-known technology regardingthe back coating layer can be applied, and a well-known technologyregarding the magnetic layer and/or the non-magnetic layer can also beapplied.

Non-Magnetic Layer

Next, the non-magnetic layer will be described. The magnetic tape mayinclude a magnetic layer directly on a surface of a non-magneticsupport, or may include a magnetic layer through the non-magnetic layerincluding non-magnetic powder and a binding agent on the surface of thenon-magnetic support. The non-magnetic powder used in the non-magneticlayer may be inorganic powder or organic powder. In addition, carbonblack and the like can be used. Examples of the inorganic powder includepowders of metal, metal oxide, metal carbonate, metal sulfate, metalnitride, metal carbide, and metal sulfide. These non-magnetic powder canbe purchased as a commercially available product or can be manufacturedby a well-known method. For details thereof, descriptions disclosed inparagraphs 0146 to 0150 of JP2011-216149A can be referred to. For carbonblack which can be used in the non-magnetic layer, descriptionsdisclosed in paragraphs 0040 and 0041 of JP2010-24113A can be referredto. The content (filling percentage) of the non-magnetic powder of thenon-magnetic layer is preferably 50% to 90% by mass and more preferably60% to 90% by mass.

In regards to other details of a binding agent or additives of thenon-magnetic layer, the well-known technology regarding the non-magneticlayer can be applied. In addition, in regards to the type and thecontent of the binding agent, and the type and the content of theadditive, for example, the well-known technology regarding the magneticlayer can be applied.

The non-magnetic layer of the magnetic tape also includes asubstantially non-magnetic layer including a small amount offerromagnetic powder as impurities or intentionally, together with thenon-magnetic powder. Here, the substantially non-magnetic layer is alayer having a residual magnetic flux density equal to or smaller than10 mT, a layer having coercivity equal to or smaller than 7.96 kA/m (100Oe), or a layer having a residual magnetic flux density equal to orsmaller than 10 mT and coercivity equal to or smaller than 7.96 kA/m(100 Oe). It is preferable that the non-magnetic layer does not have aresidual magnetic flux density and coercivity.

Non-Magnetic Support

Next, the non-magnetic support (hereinafter, also simply referred to asa “support”) will be described. As the non-magnetic support, well-knowncomponents such as polyethylene terephthalate, polyethylene naphthalate,polyamide, polyamide imide, aromatic polyamide subjected to biaxialstretching are used. Among these, polyethylene terephthalate,polyethylene naphthalate, and polyamide are preferable. Coronadischarge, plasma treatment, easy-bonding treatment, or heatingtreatment may be performed with respect to these supports in advance.

Various Thickness

The thickness of the non-magnetic support is preferably 3.00 to 20.00μm, more preferably 3.00 to 10.00 μm, even more preferably 3.00 to 6.00μm, and particularly preferably 3.00 to 4.50 μm.

The thickness of the magnetic layer is preferably equal to or smallerthan 0.15 μm and more preferably equal to or smaller than 0.10 μm, froma viewpoint of realizing recording at high density which is recentlyrequired. The thickness of the magnetic layer is even more preferably0.01 to 0.10 μm. The magnetic layer may be at least single layer, themagnetic layer may be separated into two or more layers having differentmagnetic properties, and a configuration of a well-known multilayeredmagnetic layer can be applied. A thickness of the magnetic layer in acase where the magnetic layer is separated into two or more layers isthe total thickness of the layers.

A thickness of the non-magnetic layer is, for example, 0.10 to 1.50 μmand preferably 0.10 to 1.00 μm.

A thickness of the back coating layer is preferably equal to or smallerthan 0.90 μm, more preferably 0.10 to 0.70 μm, even more preferably 0.10to 0.55 μm, and still more preferably 0.10 to 0.50 μm.

The thicknesses of various layers of the magnetic tape and thenon-magnetic support can be acquired by a well-known film thicknessmeasurement method. As an example, a cross section of the magnetic tapein a thickness direction is, for example, exposed by a well-known methodof ion beams or microtome, and the exposed cross section is observedwith a scanning electron microscope. In the cross section observation,various thicknesses can be acquired as a thickness acquired at oneposition of the cross section in the thickness direction, or anarithmetical mean of thicknesses acquired at a plurality of positions oftwo or more positions, for example, two positions which are randomlyextracted. In addition, the thickness of each layer may be acquired as adesigned thickness calculated according to the manufacturing conditions.

Manufacturing Method

Preparation of Each Layer Forming Composition

Each composition for forming the magnetic layer, the back coating layer,or the non-magnetic layer, normally includes a solvent, together withvarious components described above. As the solvent, various organicsolvents generally used for manufacturing a coating type magneticrecording medium can be used. Among those, from a viewpoint ofsolubility of the binding agent normally used in the coating typemagnetic recording medium, each layer forming composition preferablyincludes one or more ketone solvents such as acetone, methyl ethylketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone,isophorone, and tetrahydrofuran. The amount of the solvent of each layerforming composition is not particularly limited, and can be set to bethe same as that of each layer forming composition of a typical coatingtype magnetic recording medium. In addition, steps of preparing acomposition for forming each layer can generally include at least akneading step, a dispersing step, and a mixing step provided before andafter these steps, if necessary. Each step may be divided into two ormore stages. All of raw materials used in the invention may be added atan initial stage or in a middle stage of each step. In addition, eachraw material may be separately added in two or more steps. For example,a binding agent may be separately added in a kneading step, a dispersingstep, and a mixing step for adjusting viscosity after the dispersion. Inthe manufacturing step of the magnetic tape, a well-known manufacturingtechnology of the related art can be used in a part or all of the steps.In the kneading step, an open kneader, a continuous kneader, a pressurekneader, or a kneader having a strong kneading force such as an extruderis preferably used. The details of the kneading processes of thesekneaders are disclosed in JP1989-106338A (JP-H01-106338A) andJP1989-79274A (JP-H01-79274A). As a dispersing machine, a well-knowndispersing machine can be used. The each layer forming composition maybe filtered by a well-known method before performing the coating step.The filtering can be performed by using a filter, for example. As thefilter used in the filtering, a filter having a hole diameter of 0.01 to3 μm (for example, filter made of glass fiber or filter made ofpolypropylene) can be used, for example.

Regarding the dispersion process of the magnetic layer formingcomposition, it is preferable to prevent the occurrence of chipping asdescribed above. In order to realize the prevention, it is preferable toperform the dispersion process of the ferromagnetic hexagonal ferritepowder by a dispersion process having two stages, in which a coarseaggregate of the ferromagnetic hexagonal ferrite powder is crushed bythe dispersion process in a first stage, and the dispersion process in asecond stage, in which a collision energy applied to particles of theferromagnetic hexagonal ferrite powder due to collision with thedispersion beads is smaller than that in the first dispersion process,is performed, in the step of preparing the magnetic layer formingcomposition. According to such a dispersion process, it is possible toimprove dispersibility of the ferromagnetic hexagonal ferrite powder andprevent the occurrence of chipping.

As a preferred aspect of the dispersion process having two stages, adispersion process including a first stage of obtaining a dispersionliquid by performing the dispersion process of the ferromagnetichexagonal ferrite powder, the binding agent, and the solvent under thepresence of first dispersion beads, and a second stage of performing thedispersion process of the dispersion liquid obtained in the first stageunder the presence of second dispersion beads having smaller beaddiameter and density than those of the first dispersion beads can beused. Hereinafter, the dispersion process of the preferred aspectdescribed above will be further described.

In order to increase the dispersibility of the ferromagnetic hexagonalferrite powder, the first stage and the second stage are preferablyperformed as the dispersion process before mixing the ferromagnetichexagonal ferrite powder and other powder components. For example, in acase of forming the magnetic layer including the non-magnetic powder,the first stage and the second stage are preferably performed as adispersion process of a solution (magnetic liquid) includingferromagnetic hexagonal ferrite powder, a binding agent, a solvent, andrandomly added additives, before mixing the non-magnetic powder.

A bead diameter of the second dispersion bead is preferably equal to orsmaller than 1/100 and more preferably equal to or smaller than 1/500 ofa bead diameter of the first dispersion bead. The bead diameter of thesecond dispersion bead can be, for example, equal to or greater than1/10,000 of the bead diameter of the first dispersion bead. However,there is no limitation to this range. The bead diameter of the seconddispersion bead is, for example, preferably 80 to 1,000 nm. Meanwhile,the bead diameter of the first dispersion bead can be, for example, 0.2to 1.0 mm.

The bead diameter of the invention and the specification is a valuemeasured by the same method as the measurement method of the averageparticle size of the powder described above.

The second stage is preferably performed under the conditions in whichthe amount of the second dispersion beads is equal to or greater than 10times of the amount of the ferromagnetic hexagonal ferrite powder, andis more preferably performed under the conditions in which the amount ofthe second dispersion beads is 10 times to 30 times of the amount of theferromagnetic hexagonal ferrite powder, based on mass.

Meanwhile, the amount of the dispersion beads in the first stage ispreferably in the range described above.

The second dispersion beads are beads having lower density than that ofthe first dispersion beads. The “density” is obtained by dividing themass (unit: g) of the dispersion beads by volume (unit: cm³). Themeasurement is performed by the Archimedes method. The density of thesecond dispersion beads is preferably equal to or lower than 3.7 g/cm³and more preferably equal to or lower than 3.5 g/cm³. The density of thesecond dispersion beads may be, for example, equal to or higher than 2.0g/cm³ or may be lower than 2.0 g/cm³. As the preferred second dispersionbeads from a viewpoint of density, diamond beads, silicon carbide beads,or silicon nitride beads can be used, and as preferred second dispersionbeads from a viewpoint of density and hardness, diamond beads can beused.

Meanwhile, as the first dispersion beads, dispersion beads havingdensity exceeding 3.7 g/cm³ are preferable, dispersion beads havingdensity equal to or higher than 3.8 g/cm³ are more preferable, anddispersion beads having density equal to or higher than 4.0 g/cm³ areeven more preferable. The density of the first dispersion beads may be,for example, equal to or smaller than 7.0 g/cm³ or may exceed 7.0 g/cm³.As the first dispersion beads, zirconia beads or alumina beads arepreferably used, and zirconia beads are more preferably used.

The dispersion time is not particularly limited and may be set inaccordance with the kind of a dispersing machine used.

Coating Step

The magnetic layer can be formed by directly applying the magnetic layerforming composition onto the surface of the non-magnetic support or byperforming multilayer coating of the magnetic layer forming compositionwith the non-magnetic layer forming composition in order or at the sametime. The back coating layer can be formed by applying the back coatinglayer forming composition to a surface side of the non-magnetic supportopposite to a side provided with the magnetic layer (or to be providedwith the magnetic layer). For details of the coating for forming eachlayer, a description disclosed in paragraph 0066 of JP2010-231843A canbe referred to.

Other Steps

For details of various other steps for manufacturing the magnetic tape,descriptions disclosed in paragraphs 0067 to 0070 of JP2010-231843A canbe referred to. For example, preferably, while the coating layer of themagnetic layer forming composition is wet, an alignment process of theferromagnetic hexagonal ferrite powder in the coating layer is performedin an alignment zone. For the alignment process, various well-knowntechnologies such as a description disclosed in a paragraph 0067 ofJP2010-231843A can be used. As described above, it is preferable toperform the homeotropic alignment process as the alignment process, froma viewpoint of controlling the XRD intensity ratio. Regarding thealignment process, the above description can also be referred to. Inaddition, it is also preferable that the surface smoothing treatment isperformed. The smoothness of the surface of the magnetic layer of themagnetic tape can be increased by the surface smoothing treatment. Thesurface smoothing treatment is preferably performed by a calenderprocess. For details of the calender process, for example, descriptiondisclosed in a paragraph 0026 of JP2010-231843A can be referred to. Asthe calender process is reinforced, the surface of the magnetic tape canbe smoothened (that is, the value of the magnetic layer surfaceroughness Ra can be decreased). The calender process is reinforced, asthe surface temperature (calender temperature) of a calender roll isincreased and/or as calender pressure is increased.

One Aspect of Preferred Manufacturing Method

As a preferred manufacturing method, a manufacturing method of applyingvibration to the back coating layer in any stage after applying the backcoating layer forming composition can be used, in order to improveuniformity of the thickness of the liquid film of fatty acid ester onthe surface of the back coating layer of the magnetic tape. Thevibration application can be performed in any stage that is after dryingor curing the coating layer of the back coating layer formingcomposition. It is thought that, by adding vibration, the liquid film offatty acid ester on the surface of the coating layer flows and theuniformity of the thickness of the liquid film of fatty acid ester onthe surface of the back coating layer to be formed is improved. It issurmised that it is preferable to improve uniformity of the thickness ofthe liquid film, in order to control the FWHM_(before) to be greaterthan 0 nm and equal to or smaller than 10.0 nm. That is, in one aspectof the preferable manufacturing method, a back coating layer formingstep including, applying the back coating layer forming compositionincluding non-magnetic powder, a binding agent, and fatty acid ester onone surface side of the non-magnetic support and drying to form acoating layer, and applying vibration to the formed coating layercoating layer to form the back coating layer. The manufacturing step isidentical to the typical manufacturing step of the magnetic tape, exceptfor applying vibration to the coating layer of the back coating layerforming composition, and the details thereof are as described above.

Means for applying vibration are not particularly limited. For example,the vibration can be applied to the back coating layer by bringing thesurface of the non-magnetic support, to which the back coating layerforming composition is applied, on a side opposite to the back coatinglayer, into contact with a vibration imparting unit. The non-magneticsupport, provided with the back coating layer formed, may run whilecoming into contact with a vibration imparting unit. The vibrationimparting unit, for example, includes an ultrasonic vibrator therein,and accordingly, vibration can be applied to a product coming intocontact with the unit. It is possible to adjust the vibration applied tothe back coating layer by a vibration frequency and strength of theultrasonic vibrator, and/or the contact time with the vibrationimparting unit. For example, the contact time can be adjusted by arunning speed of the non-magnetic support, provided with the backcoating layer formed, while coming into contact with the vibrationimparting unit. The vibration imparting conditions are not particularlylimited, and may be set so as to control the full width at half maximumof the spacing distribution described above, particularly, theFWHM_(before) measured before vacuum heating. In order to set thevibration imparting conditions, a preliminary experiment can beperformed before the actual manufacturing, and the conditions can beoptimized.

As described above, it is possible to obtain a magnetic tape included inthe magnetic tape device according to one aspect of the invention.However, the manufacturing method described above is merely an example,the magnetic layer surface roughness Ra, the XRD intensity ratio, thevertical squareness ratio, the FWHM_(before) and the FWHM_(after) of theback coating layer, and the difference (S_(after)−S_(before)) can becontrolled to be in respective ranges described above by a random methodcapable of adjusting the magnetic layer surface roughness Ra, the XRDintensity ratio, the vertical squareness ratio, and the logarithmicdecrement, and such an aspect is also included in the invention. Themagnetic tape is generally accommodated in a magnetic tape cartridge andthe magnetic tape cartridge is mounted in the magnetic tape device(drive). A servo pattern can also be formed in the magnetic tape by awell-known method, in order to allow head tracking servo to be performedin the drive. The drive includes at least the magnetic tape mounted onthe magnetic tape cartridge, and one or more magnetic heads forrecording and/or reproducing information. Even in a case where themagnetic tape is allowed to run in the drive and feeding and winding ofthe magnetic tape from a reel of the magnetic tape cartridge arerepeated, it is possible to prevent the occurrence of the edge damage,according to the magnetic tape according to one aspect of the invention.In addition, as a running speed of the magnetic tape in the driveincreases, the recording of information and reproducing of the recordedinformation can be performed for a short time. Here, the running speedof the magnetic tape is a relative speed of the magnetic tape and themagnetic head in the drive and is normally set in a controller of thedrive. As the running speed of the magnetic tape increases, the contactstate between the surface of the magnetic layer and the surface of theback coating layer tends to be unstable, and accordingly, the edgedamage easily occurs. Even in such a case, it is possible to prevent theoccurrence of the edge damage, according to the magnetic tape accordingto one aspect of the invention. The magnetic tape according to oneaspect of the invention is suitably used in a drive in which the runningspeed of the magnetic tape is equal to or higher than 3 m/sec (forexample, 3 to 20 m/sec).

EXAMPLES

Hereinafter, the invention will be described with reference to examples.However, the invention is not limited to aspects shown in the examples.“Parts” and “%” in the following description mean “parts by mass” and “%by mass”, unless otherwise noted. In addition, steps and evaluationsdescribed below are performed in an environment of an atmospheretemperature of 23° C.±1° C., unless otherwise noted.

1. Manufacturing of Magnetic Tape Example 1

A list of each layer forming composition is shown below.

List of Magnetic Layer Forming Composition

Magnetic Liquid

Plate-shaped ferromagnetic hexagonal ferrite powder (M-type bariumferrite): 100.0 parts

-   -   (Activation volume: 1,500 nm³)

Oleic acid: 2.0 parts

A vinyl chloride copolymer (MR-104 manufactured by Zeon Corporation):10.0 parts SO₃Na group-containing polyurethane resin: 4.0 parts

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.07        meq/g)

An amine-based polymer (DISPERBYK-102 manufactured by BYK Additives &Instruments): 6.0 parts

Methyl ethyl ketone: 150.0 parts

Cyclohexanone: 150.0 parts

Abrasive Solution

α-alumina: 6.0 parts

-   -   (BET specific surface area: 19 m²/g, Mohs hardness: 9)

SO₃Na group-containing polyurethane resin: 0.6 parts

-   -   (Weight-average molecular weight: 70,000, SO₃Na group: 0.1        meq/g)

2,3-Dihydroxynaphthalene: 0.6 parts

Cyclohexanone: 23.0 parts

Projection Formation Agent Liquid

Colloidal silica: 2.0 parts

-   -   (Average particle size: 80 nm)

Methyl ethyl ketone: 8.0 parts

Lubricant and Curing Agent Liquid

Stearic acid: 3.0 parts

Stearic acid amide: 0.3 parts

Butyl stearate: 6.0 parts

Methyl ethyl ketone: 110.0 parts

Cyclohexanone: 110.0 parts

Polyisocyanate (CORONATE (registered trademark) L manufactured by TosohCorporation): 3.0 parts

List of Non-Magnetic Layer Forming Composition

Non-magnetic inorganic powder: α-iron oxide: 100.0 parts

-   -   (Average particle size: 10 nm, BET specific surface area: 75        m²/g)

Carbon black: 25.0 parts

-   -   (Average particle size: 20 nm)

A SO₃Na group-containing polyurethane resin: 18.0 parts

-   -   (Weight-average molecular weight: 70,000, content of SO₃Na        group: 0.2 meq/g)

Stearic acid: 1.0 parts

Cyclohexanone: 300.0 parts

Methyl ethyl ketone: 300.0 parts

List of Back Coating Layer Forming Composition

Non-magnetic powder: 100.0 parts

-   -   inorganic powder (α-iron oxide): see Table 1 for ratio    -   (Average particle size: 150 nm, Average acicular ratio: 7, BET        specific surface area: 52 m²/g)    -   Carbon black: see Table 1 for ratio    -   (Average particle size: 20 nm)

A vinyl chloride copolymer: 13.0 parts

A sulfonic acid salt group-containing polyurethane resin: 6.0 parts

Phenylphosphonic acid: 3.0 parts

Cyclohexanone: 140.0 parts

Methyl ethyl ketone: 170.0 parts

Butyl stearate: see Table 1

Stearic acid: 2.0 parts

Polyisocyanate (CORONATE L manufactured by Tosoh Corporation): 5.0 parts

Methyl ethyl ketone: 400.0 parts

Preparation of Magnetic Layer Forming Composition

The magnetic layer forming composition was prepared by the followingmethod.

A dispersion liquid A was prepared by dispersing (first stage) variouscomponents of the magnetic liquid with a batch type vertical sand millby using zirconia beads having a bead diameter of 0.5 mm (firstdispersion beads, density of 6.0 g/cm³) for 24 hours, and thenperforming filtering with a filter having a hole diameter of 0.5 μm. Theused amount of zirconia beads was 10 times of the amount of theferromagnetic hexagonal barium ferrite powder based on mass.

After that, a dispersion liquid (dispersion liquid B) was prepared bydispersing (second stage) dispersion liquid A with a batch type verticalsand mill by using diamond beads having a bead diameter shown in Table 1(second dispersion beads, density of 3.5 g/cm³) for 1 hour, and thenseparating diamond beads by using a centrifugal separator. The magneticliquid is the dispersion liquid B obtained as described above. The usedamount of diamond beads was 10 times of the amount of the ferromagnetichexagonal ferrite barium powder based on mass.

Regarding the abrasive solution, various components of the abrasivesolution were mixed with each other and put in a transverse beads milldisperser together with zirconia beads having a bead diameter of 0.3 mm,so as to perform the adjustment so that a value of bead volume/(abrasivesolution volume+bead volume) was 80%, the beads mill dispersion processwas performed for 120 minutes, the liquid after the process wasextracted, and an ultrasonic dispersion filtering process was performedby using a flow type ultrasonic dispersion filtering device. By doingso, the abrasive solution was prepared.

The magnetic layer forming composition was prepared by introducing theprepared magnetic liquid, the abrasive solution, the projectionformation agent solution, and the lubricant and curing agent solution ina dissolver, stirring the mixture at a circumferential speed of 10 m/secfor 30 minutes, and performing a process of 3 passes at a flow rate of7.5 kg/min with a flow type ultrasonic disperser stirring device, andfiltering the mixture with a filter having a hole diameter of 1 μm.

The activation volume of the ferromagnetic hexagonal ferrite powderdescribed above is a value calculated by performing measurement by usingpowder which is the same powder lot as the ferromagnetic hexagonalferrite powder used in the preparation of the magnetic layer formingcomposition. The magnetic field sweep rates in the coercivity Hemeasurement part at timing points of 3 minutes and 30 minutes weremeasured by using an oscillation sample type magnetic-flux meter(manufactured by Toei Industry Co., Ltd.), and the activation volume wascalculated from the relational expression described above. Themeasurement was performed in the environment of 23° C.±1° C.

Preparation of Non-Magnetic Layer Forming Composition

A non-magnetic layer forming composition was prepared by dispersingvarious components of the non-magnetic layer forming composition with abatch type vertical sand mill by using zirconia beads having a beaddiameter of 0.1 mm for 24 hours, and then performing filtering with afilter having a hole diameter of 0.5 μm.

Preparation of Back Coating Layer Forming Composition

Components among various components of the back coating layer formingcomposition except a lubricant (butyl stearate and stearic acid),polyisocyanate, and methyl ethyl ketone (400.0 parts) were kneaded anddiluted by an open kneader, and subjected to a dispersion process with atransverse beads mill disperser. After that, the lubricant (butylstearate and stearic acid), polyisocyanate, and methyl ethyl ketone(400.0 parts) were added, stirred and mixed with a dissolver stirrer,and a back coating layer forming composition was prepared.

Manufacturing Method of Magnetic Tape

The back coating layer forming composition was applied onto one surfaceof a polyethylene naphthalate support having a thickness of 4.50 μm sothat the thickness after the drying becomes 0.50 μm, and dried, and acoating layer was formed. Then, the support, provided with the coatinglayer formed, was installed in a vibration imparting device shown inFIG. 1 so that the surface thereof on a side opposite to the surfacewhere the coating layer is formed comes into contact with the vibrationimparting unit, and the support (in FIG. 1, reference numeral 101),provided with the coating layer formed, was transported at atransportation speed of 0.5 m/sec, to apply vibration to the coatinglayer. In FIG. 1, a reference numeral 102 denotes a guide roller (areference numeral 102 denotes one of two guide rollers), a referencenumeral 103 denotes the vibration imparting device (vibration impartingunit including the ultrasonic vibrator), and an arrow denotes atransportation direction. The time from the start of the contact of thearbitrary portion of the support, provided with the coating layerformed, with the vibration imparting unit until the end of the contactis shown in Table 1 as the vibration imparting time. The vibrationimparting unit used includes an ultrasonic vibrator therein. Thevibration was imparted by setting a vibration frequency and the strengthof the ultrasonic vibrator as values shown in Table 1.

After that, the non-magnetic layer forming composition was applied ontothe surface of the support provided with the back coating layer formed,on a side opposite to the surface where the back coating layer isformed, so that the thickness after the drying becomes 1.00 μm, anddried, and a non-magnetic layer was formed.

The magnetic layer forming composition was applied onto the surface ofthe formed non-magnetic layer so that the thickness after the dryingbecomes 0.10 μm, and a coating layer was formed. A homeotropic alignmentprocess was performed in the alignment zone by applying a magnetic fieldhaving strength shown in Table 1 in a vertical direction with respect tothe surface of the coating layer, while the formed coating layer is wet.Then, the coating layer was dried and a magnetic layer was formed.

A calender process (surface smoothing treatment) of the magnetic tapeobtained as described above was performed with a calender configured ofonly a metal roll, at a speed of 100 m/min, linear pressure of 300 kg/cm(294 kN/m), by using a calender roll having a surface temperature shownin Table 1, and heat treatment was performed in an environment of anatmosphere temperature of 70° C. for 36 hours. After the heat treatment,the slitting was performed so as to have a width of ½ inches (0.0127meters), and a servo pattern was formed on the magnetic layer by acommercially available servo writer.

By doing so, the magnetic tape of Example 1 was obtained.

Examples 2 to 11, Comparative Examples 1 to 11, and Reference Examples 1and 2

A magnetic tape was manufactured in the same manner as in Example 1,except that various items shown in Table 1 were changed as shown inTable 1.

The vibration imparting time was adjusted by changing the transportationspeed of the support formed with the back coating layer.

A ratio of the inorganic powder/carbon black in the back coating layershown in Table 1 is a content of each powder based on mass with respectto 100.0 parts by mass of a total content of the non-magnetic powder(inorganic powder and carbon black).

In Table 1, in the comparative examples and the reference examples inwhich “none” is shown in a column of the dispersion beads and a columnof the time, the magnetic layer forming composition was prepared withoutperforming the second stage in the magnetic liquid dispersion process.

In Table 1, in the comparative examples and the reference examples inwhich “none” is shown in a column of the homeotropic alignment processmagnetic field strength, the magnetic layer was formed withoutperforming the alignment process.

In Table 1, in the comparative examples and the reference examples inwhich “not performed” is disclosed in a column of the ultrasonicvibration imparting conditions, a magnetic tape was manufactured by amanufacturing step not performing the ultrasonic vibration imparting.

2. Various Evaluations

(1) XRD Intensity Ratio

A tape sample was cut out from the manufactured magnetic tape.

Regarding the cut-out tape sample, the surface of the magnetic layer wasirradiated with X-ray by using a thin film X-ray diffraction device(Smart Lab manufactured by Rigaku Corporation), and the In-Plane XRD wasperformed by the method described above.

The peak intensity Int(114) of the diffraction peak of the (114) planeand the peak intensity Int(110) of the diffraction peak of a (110) planeof a hexagonal ferrite crystal structure were obtained from the X-raydiffraction spectra obtained by the In-Plane XRD, and the XRD intensityratio (Int(110)/Int(114)) was calculated.

(2) Vertical Squareness Ratio

A vertical squareness ratio of the manufactured magnetic tape wasobtained by the method described above using an oscillation sample typemagnetic-flux meter (manufactured by Toei Industry Co., Ltd.).

(3) Center Line Average Surface Roughness Ra Measured Regarding Surfaceof Magnetic Layer

The measurement regarding a measurement area of 40 μm×40 μm in thesurface of the magnetic layer of the magnetic tape was performed with anatomic force microscope (AFM, Nanoscope 4 manufactured by VeecoInstruments, Inc.) in a tapping mode, and a center line average surfaceroughness Ra was acquired. RTESP-300 manufactured by BRUKER is used as aprobe, a scan speed (probe movement speed) was set as 40 μm/sec, and aresolution was set as 512 pixel×512 pixel.

(4) FWHM_(before) and FWHM_(after) of Back Coating Layer

The FWHM_(before) and FWHM_(after) were acquired by the following methodby using a tape spacing analyzer (TSA) (manufactured by Micro Physics,Inc.).

In a state where a glass sheet included in the TSA was disposed on thesurface of the back coating layer of the magnetic tape, a hemisphere waspressed against the surface of the magnetic layer of the magnetic tapeat a pressure of 5.05×10⁴ N/m (0.5 atm) by using a hemisphere made ofurethane included in the TSA as a pressing member. In this state, agiven region (150,000 to 200,000 μm²) of the surface of the back coatinglayer of the magnetic tape was irradiated with white light from astroboscope included in the TSA through the glass sheet, and theobtained reflected light was received by a charge-coupled device (CCD)through an interference filter (filter selectively passing light at awavelength of 633 nm), and thus, an interference fringe image generatedon the uneven part of the region was obtained.

This image was divided into 300,000 points, a distance (spacing) betweenthe surface of the glass sheet of each point on the magnetic tape sideand the surface of the back coating layer of the magnetic tape wasacquired, this was shown as a histogram, and the FWHM_(before) beforevacuum heating and FWHM_(after) after vacuum heating were acquired bysetting the full width at half maximum, in a case where the histogramwas fit with Gaussian distribution, as the full width at half maximum ofthe spacing distribution.

The vacuum heating was performed by storing the magnetic tape in avacuum constant temperature drying machine with a degree of vacuum of200 Pa to 0.01 Mpa and at inner atmosphere temperature of 70° C. to 90°C. for 24 hours.

(5) Difference (S_(after)−S_(before)) of Back Coating Layer

The difference (S_(after)−S_(before)) was a value obtained bysubtracting a mode of the histogram before the vacuum heating from amode of the histogram after the vacuum heating obtained in the section(4).

(6) Evaluation of Edge Damage

A magnetic tape cartridge accommodating each magnetic tape (magnetictape total length of 500 m) of the examples, the comparative examples,and the reference examples was set in a drive of Linear Tape-OpenGeneration 7 (LTO-G7) manufactured by IBM, and the magnetic tape wassubjected to reciprocating running 1,500 times at tension of 0.6 N and arunning speed of 5 m/sec, while bringing the surface of the magneticlayer into contact with the magnetic head for sliding.

The magnetic tape cartridge after the miming was set in a referencedrive (LTO-G7 drive manufactured by IBM), and the magnetic tape isallowed to run to perform the recording and reproducing. A reproductionsignal during the running was introduced to an external analog/digital(AD) conversion device. A signal having a reproducing signal amplitudewhich is decreased 70% or more than an average (average of measuredvalues at each track) respectively in a track closest to one edge of themagnetic tape and a track closest to the other edge thereof was set as amissing pulse, a generation frequency (number of times of thegeneration) thereof was divided by the total length of the magnetic tapeto obtain a missing pulse generation frequency per unit length of themagnetic tape (per 1 m) (unit: times/m).

As the edge damage heavily occurs, the missing pulse generationfrequency obtained by the method described above increases. Accordingly,the missing pulse generation frequency obtained by the method describedabove becomes an index for the edge damage. In a case where the missingpulse generation frequency is equal to or smaller than 10.0 times/m, itis possible to determine that the occurrence of the edge damage isprevented to a sufficient practical level. The position where the edgedamage occurs is not constant, and therefore, in this evaluation, themeasurement result having a large number of missing pulses was used asthe missing pulse generation frequency, among the measurement result ina track closest to one edge and the measurement result in a trackclosest to the other edge, and was shown in Table 1.

The results described above are shown in Table 1.

TABLE 1 Magnetic liquid dispersion process second stage Dispersion beadsUsed amount (mass Amount of butyl Ultrasonic vibration of beads withHomeotropic stearate in back imparting conditions respect to mass ofalignment Surface coating layer Vibration ferromagnetic processtemperature forming imparting Vibration Bcad hexagonal ferrite magneticfield of calender composition time frequency Strength Kind diameterpowder) Time strength roll (part) (second) (kHz) (W) Reference None NoneNone None None  80° C. 0.2 None None None Example 1 Reference None NoneNone None None  95° C. 0.2 None None None Example 2 Comparative NoneNone None None None 100° C. 0.2 None None None Example 1 ComparativeNone None None None None 110° C. 0.2 None None None Example 2Comparative Diamond 500 nm 10 times 1 h 0.15T 100° C. 0.2 None None NoneExample 3 Comparative Diamond 500 nm 10 times 1 h 0.15T 100° C. 0.0 0.830 100 Example 4 Comparative Diamond 500 nm 10 times 1 h 0.15T 100° C.1.2 0.8 30 100 Example 5 Comparative Diamond 500 nm 10 times 1 h 0.15T100° C. 0.2 0.8 30 100 Example 6 Comparative None None None None None100° C. 0.2 0.8 30 100 Example 7 Comparative None None None None 0.15T100° C. 0.2 0.8 30 100 Example 8 Comparative None None None None 0.30T100° C. 0.2 0.8 30 100 Example 9 Comparative Diamond 500 nm 10 times 1 h1.00T 100° C. 0.2 0.8 30 100 Example 10 Comparative Diamond 500 nm 10times 1 h None 100° C. 0.2 0.8 30 100 Example 11 Example 1 Diamond 500nm 10 times 1 h 0.15T 100° C. 0.2 0.8 30 100 Example 2 Diamond 500 nm 10times 1 h 0.15T 100° C. 0.5 0.8 30 100 Example 3 Diamond 500 nm 10 times1 h 0.15T 100° C. 1.0 0.8 30 100 Example 4 Diamond 500 nm 10 times 1 h0.20T 100° C. 0.2 0.8 30 100 Example 5 Diamond 500 nm 10 times 1 h 0.30T100° C. 0.2 0.8 30 100 Example 6 Diamond 500 nm 10 times 1 h 0.50T 100°C. 0.2 0.8 30 100 Example 7 Diamond 500 nm 20 times 1 h 0.15T 100° C.0.2 0.8 30 100 Example 8 Diamond 500 nm 10 times 1 h 0.30T 110° C. 0.20.8 30 100 Example 9 Diamond 500 nm 10 times 1 h 0.30T 110° C. 0.2 2.030 100 Example 10 Diamond 500 nm 10 times 1 h 0.30T 110° C. 0.2 0.8 30100 Example 11 Diamond 500 nm 10 times 1 h 0.30T 110° C. 0.2 2.0 30 100Ratio of Back coating Missing pulse inorganic layer XRD intensityMagnetic layer generation powder/carbon S_(after)-S_(before)FWHM_(before) FWHM_(after) ratio Vertical surface frequency black (nm)(nm) (nm) Int (110)/Int (114) squareness ratio roughness Ra (times/m)Reference 80/20 1.5 13.0 8.0 0.2 0.55 2.5 nm 3 Example 1 Reference 80/201.6 13.1 8.0 0.2 0.55 2.0 nm 4 Example 2 Comparative 80/20 1.5 13.1 7.90.2 0.55 1.8 nm 13 Example 1 Comparative 80/20 1.6 13.0 8.0 0.2 0.55 1.5nm 18 Example 2 Comparative 80/20 1.6 13.0 8.0 0.5 0.70 1.8 nm 12Example 3 Comparative 80/20 0.0 7.9 8.0 0.5 0.70 1.8 nm 12 Example 4Comparative 80/20 9.6 8.0 8.0 0.5 0.70 1.8 nm 12 Example 5 Comparative 0/100 1.7 7.9 12.0 0.5 0.70 1.8 nm 12 Example 6 Comparative 80/20 1.68.1 8.0 0.2 0.55 1.8 nm 12 Example 7 Comparative 80/20 1.6 8.0 7.9 3.80.63 1.8 nm 12 Example 8 Comparative 80/20 1.7 8.0 7.9 5.0 0.75 1.8 nm12 Example 9 Comparative 80/20 1.6 8.1 8.0 6.1 0.90 1.8 nm 12 Example 10Comparative 80/20 1.5 8.0 8.0 0.3 0.66 1.8 nm 12 Example 11 Example 180/20 1.6 7.9 8.0 0.5 0.70 1.8 nm 5 Example 2 80/20 4.0 7.9 8.0 0.5 0.701.8 nm 5 Example 3 80/20 8.0 7.9 8.0 0.5 0.70 1.8 nm 5 Example 4 80/201.6 8.0 8.0 1.5 0.75 1.8 nm 4 Example 5 80/20 1.7 8.0 8.1 2.3 0.80 1.8nm 4 Example 6 80/20 1.6 8.1 8.0 4.0 0.85 1.8 nm 4 Example 7 80/20 1.68.0 7.9 0.7 0.83 1.8 nm 5 Example 8 80/20 1.5 8.1 8.0 2.3 0.80 1.5 nm 6Example 9 80/20 1.6 2.0 8.0 2.3 0.80 1.5 nm 3 Example 10 100/0  1.6 8.02.0 2.3 0.80 1.5 nm 3 Example 11 100/0  1.6 2.0 2.0 2.3 0.80 1.5 nm 3

With the comparison of Reference Examples 1 and 2 and ComparativeExamples 1 to 11, it is possible to confirm that the edge damagesignificantly occurs, in a magnetic tape having the magnetic layersurface roughness Ra equal to or smaller than 1.8 nm (ComparativeExamples 1 to 11).

In addition, with the comparison of Examples 1 to 11 and ComparativeExamples 1 to 11, it is possible to confirm that the occurrence of theedge damage in the magnetic tape having the magnetic layer surfaceroughness Ra equal to or smaller than 1.8 nm can be prevented by settingthe XRD intensity ratio, the vertical squareness ratio, theFWHM_(before) and the FWHM_(after) of the back coating layer, and thedifference (S_(after)−S_(before)) to be in the respective rangesdescribed above.

One aspect of the invention can be effective in the technical fields ofmagnetic tapes such as back-up tapes.

What is claimed is:
 1. A magnetic tape comprising: a non-magneticsupport; a magnetic layer including ferromagnetic powder, non-magneticpowder, and a binding agent on one surface side of the non-magneticsupport; and a back coating layer including non-magnetic powder and abinding agent on the other surface side of the non-magnetic support,wherein the ferromagnetic powder is ferromagnetic hexagonal ferritepowder, a center line average surface roughness Ra measured regarding asurface of the magnetic layer is equal to or smaller than 1.8 nm, anintensity ratio Int(110)/Int(114) of a peak intensity Int(110) of adiffraction peak of a (110) plane with respect to a peak intensityInt(114) of a diffraction peak of a (114) plane of a hexagonal ferritecrystal structure obtained by an X-ray diffraction analysis of themagnetic layer by using an In-Plane method is 0.5 to 4.0, a verticalsquareness ratio of the magnetic tape is 0.65 to 1.00, the back coatinglayer includes fatty acid ester, a full width at half maximum of spacingdistribution measured by optical interferometry regarding the surface ofthe back coating layer before performing a vacuum heating with respectto the magnetic tape is greater than 0 nm and equal to or smaller than10.0 nm, a full width at half maximum of spacing distribution measuredby optical interferometry regarding the surface of the back coatinglayer after performing the vacuum heating with respect to the magnetictape is greater than 0 nm and equal to or smaller than 10.0 nm, and adifference S_(after)−S_(before) between a spacing S_(after) measured byoptical interferometry regarding the surface of the back coating layerafter performing the vacuum heating with respect to the magnetic tapeand a spacing S_(before) measured by optical interferometry regardingthe surface of the back coating layer before performing the vacuumheating with respect to the magnetic tape is greater than 0 nm and equalto or smaller than 8.0 nm.
 2. The magnetic tape according to claim 1,wherein the center line average surface roughness Ra measured regardingthe surface of the magnetic layer is 1.2 nm to 1.8 nm.
 3. The magnetictape according to claim 1, wherein the vertical squareness ratio is 0.65to 0.90.
 4. The magnetic tape according to claim 1, wherein the fullwidth at half maximum of spacing distribution measured by opticalinterferometry regarding the surface of the back coating layer beforeperforming the vacuum heating with respect to the magnetic tape isgreater than 0 nm and equal to or smaller than 8.5 nm.
 5. The magnetictape according to claim 1, wherein the full width at half maximum ofspacing distribution measured by optical interferometry regarding thesurface of the back coating layer after performing the vacuum heatingwith respect to the magnetic tape is greater than 0 nm and equal to orsmaller than 8.5 nm.
 6. The magnetic tape according to claim 1, whereinthe difference S_(after)−S_(before) is greater than 0 nm and equal to orsmaller than 6.0 nm.
 7. The magnetic tape according to claim 1, whereinthe center line average surface roughness Ra measured regarding thesurface of the magnetic layer is 1.2 nm to 1.8 nm, the verticalsquareness ratio is 0.65 to 0.90, the full width at half maximum ofspacing distribution measured by optical interferometry regarding thesurface of the back coating layer before performing the vacuum heatingwith respect to the magnetic tape is greater than 0 nm and equal to orsmaller than 8.5 nm, and the difference S_(after)−S_(before) is greaterthan 0 nm and equal to or smaller than 6.0 nm.
 8. The magnetic tapeaccording to claim 1, wherein the non-magnetic powder included in theback coating layer is one or more kinds of non-magnetic powder selectedfrom the group consisting of inorganic powder and carbon black.
 9. Themagnetic tape according to claim 8, wherein a content of the inorganicpowder in the back coating layer is greater than 50.0 parts by mass andequal to or smaller than 100.0 parts by mass with respect to 100.0 partsby mass of a total amount of the non-magnetic powder included in theback coating layer.
 10. The magnetic tape according to claim 1, furthercomprising: a non-magnetic layer including non-magnetic powder and abinding agent between the non-magnetic support and the magnetic layer.